Plasma spraying is a form of a thermal spraying technique for use in a coating process to coat a target surface with a coating material. Different coating materials, usually provided in a powder form, are used to provide desired surface characteristics. Materials can be chosen to provide protection against high temperatures such as ceramic coatings on gas turbines for power generation and aircraft. Metallic materials can be coated on steam turbines for protection against mechanical wear. In some instances, materials that are same or similar to the target part can be coated to the target part surface and coated part can be remachined for repairs. In other instances, materials can be chosen for their electrical properties—e.g., for their electrically conductive or insulative properties depending on the application.
Different plasma spray guns have varying power supply requirements, but can be generally divided into two types—low voltage high current (LVHC) and high voltage low current (HVLC). LVHC guns typically have small physical separation between the cathode and the anode. Voltage necessary to form an electrical arc between the cathode and the anode is directly proportional to the physical separation between the cathode and the anode. Thus, a relatively small voltage (about 100 VDC) is sufficient to form the electrical arc in LVHC guns. However, since the thermal energy of the plasma is dependent on the power, relatively high amount of current (upwards of 1000 A) is needed to provide sufficient energy. The power supply that powers LVHC guns thus operates in the LVHC mode, i.e., ≦1000 A and ≦100 VDC. Examples of the LVHC spray guns include Sulzer Metco® (registered trademark of Sulzer Metco Management AG, Zürcherstrasse 12 Winterthur CH8400, Switzerland) 7MB/9MB and O3C guns and Praxair® (registered trademark of Praxair Technology, Inc., 55 Old Ridgebury Road, Danbury, Conn. 06815) SG-100 guns.
Conversely, HVLC guns operate with larger separation between the cathode and the anode. As a result, a relatively high voltage (≦400 VDC) is required to form the electric arc. However, less current (upto 600 A) is required to generate the necessary thermal energy since power is the product of voltage and current. The HVLC guns require power supplies to operate in the HVLC mode, i.e., ˜600 A and ≦400 VDC. The HVLC guns such as the Praxair® Plazjet gun operates in the 200 kW range and Progressive Surface® 100HE® (registered service mark and trademark of Progressive Technologies, Inc., 4695 Danvers Drive SE, Kentwood, Mich. 49512) gun operates in the 100 kW range.
Unfortunately, conventional HVLC and LVHC systems are generally not compatible with each other. An LVHC plasma spray gun cannot be operated using an HVLC power supply designed for an HVLC gun. Conversely, an HVLC gun cannot be operated using an LVHC power supply designed for an LVHC gun. As a result, a shop having both types of guns must purchase and maintain two types of plasma spray systems to operate the different plasma spray gun types. This leads to high equipment cost, and also leads to lack of standardization in the shops. This is a particular problem for shops that operate globally.